1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a backlight unit using a branch-shaped light guide bar and a liquid crystal display device including the backlight unit.
2. Discussion of the Related Art
A liquid crystal display (LCD) device displays images using an interior light source. Since the liquid crystal panel does not include a light source, an additional light source is required. For example, a backlight unit including a light source is disposed under a liquid crystal panel to illuminate the liquid crystal panel.
FIG. 1 is an exploded perspective view of an edge type backlight unit 1.
As shown in FIG. 1, the backlight unit 1 includes a light source 10. For example, the light source 10 includes one of a cold cathode fluorescent lamp and a light emitting diode (LED). FIG. 1 shows the LED as the light source 10. In this instance, the backlight unit 1 may include a light frame 11 covering the light source 10.
The backlight unit 1 further includes a light guide plate 6, a diffusion plate 7, first and second light concentration plates 8 and 9, a mold frame 2, and a reflection plate 4. The light source 10 is disposed to the side of the light guide plate 6, and the light from the light source 10 is processed into planar light by the light guide plate 6. The diffusion plate 7 is disposed on or over the light guide plate 6, and the light from the light guide plate 6 is uniformly provided into a display region of a liquid crystal panel (not shown) by the diffusion plate 7. The first and second light concentration plates 8 and 9 are disposed on or over the diffusion plate 7, and the brightness of the light is improved by the first and second light concentration plates 8 and 9. The reflection plate 4 is disposed under the light guide plate 6 such that the light from the light guide plate 6 is reflected by the reflection plate 4. The mold frame 2 is disposed under the reflection plate 4 and accommodates the above elements. The light source 10 is fixed by the mold frame 2 and the light frame 11.
A backlight unit 1 having the above structure may be referred to as an edge type backlight unit 1. The edge type backlight unit 1 has an advantage in reduced thickness. However, since the edge type backlight unit requires the light guide plate 6, the weight of the backlight unit is increased. In addition, movement or thermal expansion of the light guide plate 6 may decrease the light uniformity of the edge type backlight unit 1. To resolve the above problems, a direct type backlight unit is introduced.
FIG. 2 is an exploded perspective view of a direct type backlight unit 20.
As shown in FIG. 2, the direct type backlight unit 20 includes a light source 10 under a liquid crystal panel (not shown) without a light guide plate 6 (of FIG. 1). For example, the light source 10 includes one of a cold cathode fluorescent lamp and a LED. FIG. 1 shows the LED as the light source 10.
The light source 10 is disposed on a bottom surface of a mold frame 2, and a diffusion plate 7 and first and second light concentration plates 8 and 9 are disposed over the light source 10. The backlight unit 20 further includes a reflection plate 4 on the mold frame 2. The reflection plate 4 includes a through hole for the light source 10.
Since the direct type backlight unit 20 in FIG. 2 does not include the light guide plate 6 (of FIG. 1), the uniformity of the light provided by the direct type backlight unit 20 is improved. However, in the direct type backlight unit 20, the diffusion plate 7 should be spaced apart from the light source by a pre-determined distance, e.g., an optical gap, for light mixing, which increases the thickness of the direct type backlight unit 20.